Propylene polymers and process for the production thereof

ABSTRACT

Propylene block copolymer containing per: 
     100 parts by weight of a polymer (a) of propylene chosen from homopolymers and copolymers of propylene not containing more than 6% by weight of ethylene and/or of an alpha-olefin having from 4 to 6 carbon atoms, 
     from 1 to 100 parts by weight of a polymer (b) of ethylene chosen from homopolymers and copolymers of ethylene not containing more than 90% by weight of propylene and/or of another alpha-olefin having from 4 to 6 carbon atoms, 
     the said block copolymer additionally containing from approximately 0.001 to approximately 20% by weight of α,ω-diene-derived monomer units with respect to the total weight of the block copolymer.

FIELD OF THE INVENTION

The present invention relates to propylene block copolymers containing anon-conjugated α,ω-diene. It more particularly relates to propyleneblock copolymers containing a non-conjugated α,ω-diene in at least oneof the blocks and to a process for the production of these copolymers.

TECHNOLOGY REVIEW

It is known to increase the impact strength of polypropylene by mixingit with ethylene-propylene elastomers. Nevertheless, as such mixturesare not perfectly homogeneous, they do not exhibit all the desiredproperties.

Attempts have been made to overcome this problem by copolymerizingpropylene with another alpha-olefin, such as, for example, ethylene.

Among propylene copolymers, those which exhibit the best impactstrength/stiffness compromise are the copolymers, known as blockcopolymers, prepared in two-stage processes comprising a first stage ofhomopolymerization of the propylene or of copolymerization of thepropylene with a maximum of 6 molar % of another alpha-olefin, such asethylene, followed by a second stage of polymerization of ethylene or ofcopolymerization of ethylene with propylene and optionally anotheralpha-olefin in proportions such that the amount of ethylene is greaterthan 10 molar % (see, for example, EP-0,202,946).

The rheological properties of these block copolymers and in particulartheir melt strength remain unsatisfactory however for specificapplications, such as thermoforming or the production of foams.

In addition, when the block copolymers are obtained by polymerization ina diluent, such as a hydrocarbon or one of the monomers maintained inthe liquid state, the formation of a significant amount ofdiluent-soluble polymer is observed in the second polymerization stage,which results in an increase in the viscosity of the polymerizationmixture, a deterioration in heat exchanges and agglomeration of thepolymer particles with each other or on the walls of the reactor. Underthese conditions, it is necessary to limit the amount of polymerproduced during this stage, which results in a limitation on the impactstrength of the final copolymers. The loss of polymer by solubilizationis also responsible for a substantial increase in production costs.

Moreover, the document JP 59/155416 discloses propylene block copolymersin which each of the blocks contains from 1 to 30% by weight of 4- or5-methyl-1,4-hexadiene. These copolymers exhibit good impact strengthand are chemically reactive.

SUMMARY OF THE INVENTION

The present invention relates to propylene block copolymers which aredifferent from those described in the prior art and which exhibit manyadvantages with respect to the latter.

To this end, the present invention relates to a propylene blockcopolymer containing per:

100 parts by weight of a polymer (a) of propylene chosen fromhomopolymers and copolymers of propylene not containing more than 6% byweight of ethylene and/or of an alpha-olefin having from 4 to 6 carbonatoms,

from 1 to 100 parts by weight of a polymer (b) of ethylene chosen fromhomopolymers and copolymers of ethylene not containing more than 90% byweight of propylene and/or of another alpha-olefin having from 4 to 6carbon atoms,

the said block copolymer additionally containing from approximately0.001 to approximately 20% by weight of α,ω-diene-derived monomer unitswith respect to the total weight of the block copolymer.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE illustrates the variation in the elongational viscosity inthe molten state (expressed in Pa.s) as a function of the elongationtime (expressed in s) for elongation rate gradients of 0.1 s⁻¹.

DETAILED DESCRIPTION OF THE INVENTION

The propylene block copolymers according to the present invention mostoften contain at least 5 parts by weight and preferably at least 10parts by weight of polymer (b) per 100 parts by weight of polymer (a).The copolymers according to the invention which contain at least 20parts by weight of polymer (b) per 100 parts by weight of polymer (a)give good results. The amount of polymer (b) is in addition notgenerally greater than 90 parts by weight. Good results are obtainedwhen the amount of polymer (b) is less than or equal to 80 parts byweight per 100 parts of polymer (a).

The polymer (a) is generally a homopolymer of propylene or a copolymerof propylene and of ethylene not containing more than 3% by weight ofethylene. Good results are obtained when the polymer (a) is ahomopolymer of propylene.

The polymer (b) is generally a copolymer of ethylene. It is most often acopolymer of ethylene containing at least 30%, preferably at least 40%,by weight of propylene. The propylene concentration in the polymer (b)is in addition generally less than or equal to 70% by weight, moreparticularly less than or equal to 60% by weight.

The block copolymers according to the present invention contain, inaddition to the monomer units derived from propylene, from ethylene andoptionally from an alpha-olefin, from approximately 0.001 toapproximately 20% by weight of monomer units derived from an α,ω-dienewith respect to the total weight of the block copolymer.

α,ω-Dienes denote diolefins containing two end carbon-carbon doublebonds. The α,ω-dienes which can be used in the block copolymersaccording to the invention generally contain from 6 to 30 carbon atoms.The preferred α,ω-dienes contain at least 7 carbon atoms. Most often,they do not contain more than 15 carbon atoms. Mention may be made, asexamples of these compounds, of 1,6-heptadiene, 1,7-octadiene,1,8-nonadiene, 1,9-decadiene, 1,10-undecadiene, 1,11-dodecadiene,1,12-tridecadiene and 1,13-tetradecadiene. Among these compounds,1,7-octadiene, 1,8-nonadiene and 1,9-decadiene give good results.1,9-Decadiene is more particularly preferred.

It is obvious that the block copolymers according to the invention whichcontain monomer units derived from one or from a number of α,ω-dienesalso come within the scope of the present invention.

The concentration of α,ω-diene-derived monomer units in the blockcopolymers according to the present invention is generally greater thanor equal to approximately 0.01% by weight with respect to the totalweight of the block copolymer. This concentration is preferably greaterthan or equal to approximately 0.02% by weight with respect to the totalweight of the block copolymer. Most often, the concentration ofα,ω-diene-derived monomer units is less than or equal to approximately10% by weight with respect to the total weight of the block copolymer.Good results are obtained when it is not greater than approximately 5%by weight with respect to the total weight of the block copolymer. Theblock copolymers in which the concentration of α,ω-diene-derived monomerunits is from 0.02 to 10% by weight with respect to their total weightare highly suitable.

The preferred block copolymers are generally such that theα,ω-diene-derived monomer units are present solely in the polymer (b).

Consequently, the propylene block copolymers according to the presentinvention most often contain per:

100 parts by weight of a polymer (a) of propylene chosen fromhomopolymers and copolymers of propylene not containing more than 6% byweight of ethylene and/or of an alpha-olefin having from 4 to 6 carbonatoms,

from 1 to 100 parts by weight of a polymer (b) of ethylene chosen fromethylene copolymers containing at least 30% and not more than 70% byweight of propylene and additionally containing from approximately 0.001to approximately 20% by weight of α,ωdiene-derived monomer units withrespect to the total weight of the block copolymer.

Very particularly preferred block copolymers contain per:

100 parts by weight of a polymer (a) which is a homopolymer ofpropylene,

from 10 to 80 parts by weight of a polymer (b) which is an ethylenecopolymer containing from 40 to 60% by weight of propylene and inaddition from approximately 0.02 to approximately 5% by weight ofmonomer units derived from an α,ω-diene.

The block copolymers according to the present invention possess theusual properties of block copolymers, such as a good stiffness/impactstrength compromise, good impact strength at low temperature, and thelike. The stiffness/impact strength compromise of the block copolymersaccording to the invention is generally superior to that of the blockcopolymers in which the first block is a propylene homopolymer and inwhich the second block is a propylene-ethylene elastomer.

They in addition exhibit, due to the presence of monomer units derivedfrom the α,ω-diene, a relatively large number of branchings whichconfers on them a good melt strength characterized by a highelongational viscosity at low rate gradient.

These block copolymers also exhibit, in the molten state, an increase inthe resistance to deformation during elongation or extension. Such aphenomenon is generally known as "stress hardening". It can easily becharacterized by determining, for a given temperature and a givenelongation rate, the variation in the elongational viscosity of theblock copolymer in the molten state as a function of the elongationtime. When subjected to such tests, the block copolymers according tothe present invention exhibit an increase in the elongational viscosityuntil the molten polymer mass ruptures, this rupture generally beingbrittle.

When subjected to these same tests, the block copolymers of the priorart do not exhibit such a phenomenon.

These different properties make the block copolymers according to thepresent invention particularly suitable for being shaped by extrusion orby injection and in particular by extrusion blow-moulding or injectionblow-moulding. These block copolymers are also suitable for being usedby thermoforming or coating. They are also highly suitable for theformation of foams.

The block copolymers according to the present invention in additionexhibit a wide range of melt flow indices (MFI, measured according toASTM standard D 1238 (1986)) and can exhibit smaller MFI values thanthose usually encountered for the block copolymers of the prior art. Forthis reason, the block copolymers according to the present inventionwhich exhibit an MFI of less than 1 g/10 min, in particular of less than0.7 and more particularly of less than 0.4 g/10 min, constitute anadditional aspect of the invention. These specific block copolymers areparticularly well suited to applications requiring very good meltstrength, as described above.

Finally, the block copolymers according to the present inventiongenerally also exhibit unsaturations arising from the incorporation, inthe polymer chains, of the α,ω-diene-derived units. These unsaturationsmake it possible to graft polar monomers, such as, as non-limitingexample, maleic anhydride, without significant degradation of thepolymer. It is thus possible to improve the printability properties ofthe block copolymers, their adhesion to different substrates and theadhesion of paint on the articles obtained from these block copolymers.These unsaturations can also be used to obtain, by appropriate means,good compatibility between the polymers (a) and (b) constituting theblock copolymer.

Such uses consequently also constitute additional aspects of the presentinvention.

The present invention also relates to a process for producing theseblock copolymers. The block copolymers according to the presentinvention are generally obtained according to a process comprising atleast two successive polymerization stages during which the polymers (a)and (b) are respectively formed.

The process according to the present invention consequently comprises atleast two successive polymerization stages in which use is made, underpolymerizing conditions, in the presence of a catalytic system, ofmixtures of monomers containing:

in the first stage, propylene and optionally up to approximately 5% byweight of ethylene and/or of an alpha-olefin having from 4 to 6 carbonatoms and/or up to approximately 50% by weight of α,ω-diene with respectto the combined monomers used in this stage, and

in the second stage, ethylene and optionally up to 95% by weight ofpropylene and/or of another alpha-olefin having from 4 to 6 carbon atomsand/or up to approximately 50% by weight of α,ω-diene with respect tothe combined monomers used in this stage, at least one of these twostages being carried out while making use of a mixture of monomerscontaining at least 0.005% by weight of α,ω-diene.

The minimum amount of α,ω-diene used in at least one of these two stagesis generally approximately 0.01% by weight and more particularlyapproximately 0.1% by weight.

The amount of α,ω-diene used in at least one of these two stagesgenerally does not exceed 30% by weight and more particularly does notexceed 20% by weight of the mixture of monomers used in this or thesestages.

Generally, the α,ω-diene is used at least in the second polymerizationstage. Processes giving good results are such that use is made, asmonomers, of:

in the first stage, propylene which can optionally contain up toapproximately 5% by weight of ethylene and/or of an alpha-olefin havingfrom 4 to 6 carbon atoms and/or up to approximately 50% by weight ofα,ω-diene with respect to the combined monomers used, and

in the second stage, a mixture of ethylene, of propylene and ofα,ω-diene containing up to approximately 90% by weight of propylene andup to approximately 50% by weight of α,ω-diene with respect to thecombined monomers used in this stage.

The amount of propylene used in this second stage is in addition mostoften at least approximately 50% by weight and more particularly atleast approximately 80% by weight.

The α,ω-diene is preferably used exclusively in the secondpolymerization stage.

The process according to the present invention is generally carried outso that, in the second stage, from 1 to 100 parts by weight of polymerare formed per 100 parts by weight of polymer formed in the first stage.

The first and the second stage are in addition most often carried outunder conditions such that the respective amounts of polymer formed arethose described above with respect to the polymers (a) and (b) of theblock copolymers according to the invention.

The two polymerization stages of the process according to the inventioncan be carried out successively in the same reactor. The second stage isthen carried out in the presence of the polymer formed in the firststage and after having completely or partially removed the unreactedmonomers. These two stages can also be carried out in two reactorsarranged in series. The second stage is then carried out in the secondreactor in the presence of the polymer formed in the first stage andafter having completely or partially removed the unreacted monomersarising from the first reactor.

The polymerization process according to the present invention isadvantageously carried out in two reactors in series.

The first stage of the process according to the present invention isgenerally carried out in the absence of alpha-olefin having 4 to 6carbon atoms. In addition, good results are obtained when use is notmade of ethylene when this stage is carried out.

The first stage of the process according to the invention is preferablya stage of homopolymerization of propylene.

The monomers used during the second stage are generally ethylene,propylene and the α,ω-diene. Moreover, good results are obtained whenthe respective amounts of ethylene and of propylene used are such thatthe ratio by weight of these monomers in the polymer formed during thisstage is greater than or equal to 0.4 and more particularly greater thanor equal to 0.65. In addition, these amounts are most often such thatthe ratio by weight of these monomers in the polymer formed during thisstage is less than or equal to 2.4, preferably less than or equal to1.5.

The amount of α,ω-diene used in the process according to the inventionis generally such that the overall composition of the block copolymerwhich is formed therein is that described above with respect to theblock copolymers according to the invention.

In the processes according to the present invention, the polymerizationcan be carried out according to any known process. This polymerizationcan be carried out in solution or in suspension in an inert hydrocarbondiluent generally chosen from liquid aliphatic, cycloaliphatic andaromatic hydrocarbons such as, for example, liquid alkanes andisoalkanes, benzene and its derivatives. Hydrocarbon diluentspreferentially used are: butane, isobutane, hexane, heptane,cyclohexane, methylcyclohexane or their mixtures. Hexane and heptane arehighly suitable. It is also possible to carry out the polymerization inthe monomer or in one of the monomers maintained in the liquid state oralternatively in the gas phase.

It is also possible to carry out the first and the second stageaccording to two different processes.

Advantageously, at least the second stage is carried out in suspensionin a hydrocarbon solvent such as described above.

The polymerization temperature is generally chosen from 20° to 200° C.and preferably from 50° to 90° C. The pressure is most often chosenbetween atmospheric pressure and 50 atmospheres. The temperature and thepressure are, of course, a function of one another and of the nature ofthe polymerization process used.

The preferred process according to the present invention comprises twopolymerization stages carried out in suspension in a hydrocarbonsolvent.

In this specific case, the amounts of monomers used in the first stageare such that the ratio of the molar fractions of ethylene and ofpropylene in the liquid phase is less than or equal to approximately0.015 and the ratio of the molar fractions of α,ωdiene and of propylenein the liquid phase is less than or equal to approximately 5.

Moreover, the amounts of monomers used in the second stage are such thatthe ratio of the molar fractions of ethylene and of propylene in theliquid phase is greater than or equal to approximately 0.06 and lessthan or equal to approximately 0.14 and the ratio of the molar fractionsof α,ω-diene and of propylene in the liquid phase is less than or equalto 5.

Good results are obtained when the amounts of monomers used forproducing the block copolymers according to the invention are such that:

in the first stage, the ratio of the molar fractions of ethylene and ofpropylene in the liquid phase is less than or equal to approximately0.015 and the ratio of the molar fractions of α,ω-diene and of propylenein the liquid phase is less than or equal to approximately 5, and

in the second stage, the ratio of the molar fractions of ethylene and ofpropylene in the liquid phase is greater than or equal to approximately0.06 and less than or equal to approximately 0.14 and the ratio of themolar fractions of α,ω-diene and of propylene in the liquid phase isless than or equal to approximately 5.

In the first stage, the ratio of the molar fractions of ethylene and ofpropylene in the liquid phase is preferably less than or equal toapproximately 0.006. When use is made of an α,ω-diene in the firststage, the amounts of monomers used are most often such that the ratioof the molar fractions of α,ω-diene and of propylene in the liquid phaseis less than or equal to approximately 2.5 and more particularly lessthan or equal to approximately 1.5. Preferably, ethylene is not used.Good results are obtained when α,ω-diene is not used in the first stage.The best results are obtained when exclusively propylene is used in thefirst stage.

In the second stage, the ratio of the molar fractions of ethylene and ofpropylene in the liquid phase is preferably less than or equal toapproximately 0.12. In addition, it is most often greater than or equalto approximately 0.08. The amounts of α,ω-diene used in this secondstage are most often such that the ratio of the molar fractions ofα,ω-diene and of propylene in the liquid phase is less than or equal toapproximately 2.5, more particularly less than or equal to approximately1.5. In addition, this ratio is generally at least 2×10⁻⁴, most often atleast 2×10⁻³ and preferably at least 5×10⁻³.

When the polymerization is carried out in a hydrocarbon diluent, it isnoticed, surprisingly, that the presence of the α,ω-diene results in adecrease in the amount of polymer soluble in the polymerization mixture.Such behaviour is particularly advantageous during the production of thepolymer (b). In fact, it makes possible greater incorporation of theelastomer block in the final block copolymer, without problems ofadhesion of the polymer particles to one another and/or on the walls ofthe reactor being observed. Block copolymers are thus easily obtained,containing a greater proportion of elastomer fraction, which possess aparticularly high impact strength. Such a phenomenon is also observedwhen the polymerization is carried out in one of the monomers maintainedin the liquid state.

Moreover, at a constant content of polymer (b), the block copolymerswhich contain an α,ω-diene are obtained with a better economical yieldand exhibit a better morphology.

The catalytic systems which can be used in the processes according tothe present invention generally comprise a catalytic solid comprising atleast one transition metal belonging to the group IVb of the PeriodicTable and an activator generally chosen from organoaluminium compounds.

These catalytic systems are well known to the person skilled in the art.

The preferred catalytic systems according to the present inventioncontain, as catalytic solid, a complexed solid based on titaniumtrichloride (TiCl₃) as described, for example, in United States PatentsU.S. Pat. No. 4,210,738, U.S. Pat. No. 4,210,736 and U.S. Pat. No.5,206,198 (Solvay) and in Patent Application EP-A-261,727 (Solvay), thecontents of which are incorporated by reference in the presentdescription. It proves to be advantageous, in order to obtain blockcopolymers exhibiting a particularly beautiful morphology, to usecatalytic solids which have in addition been subjected to aprepolymerization treatment which comprises bringing them into contactwith an alpha-olefin, such as, preferably, propylene or ethylene, underpolymerizing conditions, so as to obtain solids containing at least 50%by weight of polymer with respect to the weight of titanium chloride.The maximum amount of prepolymer is not critical. For economicalreasons, it is preferable for it not to be greater than 2000% by weightwith respect to the TiCl₃. The amount of polymer produced during thisstage is preferably greater than 100 g per kg of TiCl₃. Amounts ofprepolymer of less than 1000 g per kg of TiCl₃ give satisfactoryresults. The prepolymerization is generally carried out at the end ofthe preparation of the catalytic solid. It can also be carried out in apolymerization stage directly preceding the stages of production of thepolymers (a) and (b).

The organoaluminium activator is generally chosen from the compoundscorresponding to the formula:

    AlR.sup.1.sub.n X.sub.3-n

in which

R¹ is a hydrocarbon radical containing from 1 to 18 carbon atoms;

X is a halogen; and

n is a number such that 0<n≦3.

Surprisingly, it is found that, when the catalytic solid is a solidbased on TiCl₃, the properties of the block copolymers depend on thenature of the catalytic system used in their production and inparticular on the nature of the organoaluminium activator.

Thus, generally, the use of a halogenated organoaluminium activatorresults in block copolymers preferentially exhibiting branched polymerchains which confer on them the advantageous rheological properties alsodescribed above.

Moreover, the use of a non-halogenated organoaluminium activator, suchas, for example, a trialkylaluminium, in addition promotes the presenceof unsaturations in the polymer chains which gives rise, optionallyafter chemical conversion, to the adhesion and printability propertiesdescribed above.

For this reason, the production process according to the presentinvention has the advantage of being able, by simple modification of thenature of the activator, to result in the production of block copolymersexhibiting different properties.

The catalytic systems which can be used for the production of the blockcopolymers according to the present invention can also contain at leastone third constituent known for improving their stereospecificity and/ortheir activity.

The various constituents of the catalytic systems which can be used inthe processes according to the present invention are generally allintroduced during the first polymerization stage.

The total amount of the various constituents of the catalytic systemswhich can be used according to the present invention is not critical andforms part of what is generally known to a person skilled in the art.The total amount of activator used is generally greater than 0.1 mmolper liter of diluent, of liquid monomer or of reactor volume, preferablygreater than 0.5 mmol per liter. When the catalytic solid is a catalyticsolid based on TiCl₃, the amount of catalytic solid used is determinedas a function of its TiCl₃ content. It is most often chosen so that theconcentration of TiCl₃ in the polymerization mixture is greater than0.01 mmol per liter of diluent, of liquid monomer or of reactor volumeand preferably greater than 0.05 mmol per liter. The ratio of the amountof organoaluminium compound to the amount of catalytic solid based onTiCl₃ is generally chosen so that the molar ratio of the activator tothe TiCl₃ is between 0.5 and 20, preferably between 1 and 15. The bestresults are obtained when the molar ratio is between 2 and 12.

The average molecular mass of the block copolymers according to thepresent invention can be adjusted by the addition to the polymerizationmixture of one or a number of agents for adjusting the average molecularmass, such as hydrogen, diethylzinc, alcohols, ethers and alkyl halides.Hydrogen is particularly well suited.

EXAMPLES

The following examples serve to illustrate the invention. Theelongational viscosity of the block copolymers obtained in theseexamples is determined by means of a rheometer marketed by Rheometricsunder the name Rheometrics Extensional Rheometer RER-9000. The curves ofthe variation in the elongational viscosity in the molten state(expressed in Pa.s) as a function of the elongation time (expressed ins) for elongation rate gradients of 0.1 s⁻¹ are reproduced in the singleappended figure. These curves were recorded at 190° C. The curve 1Rrelates to Example 1R and the curves 2 and 3 relate respectively toExamples 2 and 3. The meaning of the symbols used in these examples, theunits expressing the quantities mentioned and the methods for measuringthese quantities are explained below.

prod=Catalytic productivity expressed conventionally in grams of polymerobtained per gram of TiCl₃ contained in the catalytic solid. Thisactivity is assessed indirectly from the determination of the residualtitanium content in the polymer by X-ray fluorescence.

Sol=Amount of polymer soluble in the polymerization mixture expressed as% by weight with respect to the total amount of polymer collected.

AD=Apparent density of the insoluble polymer expressed in g/dm³.

MFI=Melt flow index measured under a load of 2.16 kg at 230° C. andexpressed in g/10 min (ASTM standard D 1238 (1986)).

Flex. Mod.=Flexural modulus of the block copolymers measured accordingto ISO standard 178 (1993) expressed in MPa.

g=Torsional stiffness modulus of the block copolymers, measured at 100°C. and for an angle of torsion of 60° C. of arc, the temperature of themould being set at 70° C. and the duration of conditioning at 5 minutes(ASTM standard D 1043 (1987)). This modulus is expressed in daN/cm².

Izod=Measurement of the resilience of the polymers, expressed in kJ/m²,measured according to ISO standard 180/1A (1993).

Embrit. Temp.=Embrittlement temperature of the polymers measuredaccording to ASTM standard D 746, expressed in ° C.

EXAMPLE 1R

This example is given by way of reference. It illustrates the blockcopolymers not containing α,ω-diene.

A--Preparation of the Catalytic Solid

90 ml of hexane and 60 ml of TiCl₄ are introduced, under a nitrogenatmosphere and with stirring, into an 800 ml reactor. This hexane/TiCl₄solution is cooled to 0 (±1)° C. and a solution composed of 190 ml ofhexane and of 70 ml of diethylaluminium chloride (DEAC) is added theretoover 4 hours, a temperature of 0° C. being maintained in the reactor.

The reaction mixture, composed of a suspension of fine particles, isthen kept stirring at this temperature for 15 min, is then brought over1 hour to 25° C. and maintained for 1 hour at this temperature beforebeing brought over approximately 1 hour to 65° C. The mixture is keptstirring for 2 hours at 65° C., is then cooled to approximately 55° C.and propylene is introduced, into the gaseous head space of the reactor,under a pressure of 2 bars. This introduction is continued for a time(approximately 45 min) sufficient to obtain, per kg of final solid, 65 gof polymerized propylene. The suspension of the thus prepolymerizedsolid is then cooled to 40° C. and washed with hexane.

The reduced solid is then suspended in 456 ml of hexane and 86 ml ofdiisoamyl ether (DIAE) are added thereto. The suspension is stirred at250 rev/min for 1 hour at 50° C. and then separated by settling. Afterhaving removed the supernatant, the solid is resuspended in 210 ml ofhexane and 52 ml of TiCl₄ are added thereto. The suspension is then keptstirring (150 rev/min) at 75° C. for 2 hours. After washing, thecomplexed solid based on TiCl₃ is resuspended in hexane (in theproportion of 4 ml of hexane per gram of solid) and brought into contactwith 120 ml of a solution containing, per liter of hexane, 80 g of DEACand 176 g of n-octadecyl3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate.

On completion of addition, the suspension is kept stirring for 1 hour at30° C. before introducing propylene under a pressure of 2 bars for atime (approximately 30 min) sufficient to obtain 170 g of PP per kg offinal dry product.

The catalytic solid contains, after washing and drying, 630 g of TiCl₃per kg.

B. Preparation of the Block Copolymer

The following are introduced, under a dry nitrogen flow, into a predried5 l autoclave:

1.5 liters of hexane,

700 mg of DEAC,

20 mg of ethyl benzoate.

The autoclave is then heated to 60° C. and repressurized with propyleneto atmospheric pressure before successively introducing therein ahydrogen pressure of 1 bar, a propylene pressure of 4 bars and an amountof catalytic solid as described in part A sufficient for the amount ofTiCl₃ introduced into the reactor to be approximately 120 mg.

The reactor is maintained at 60° C. for 3 hours while supplying it withpropylene so as to keep the pressure in the reactor constant.

Under these conditions, the molar fraction of propylene in the liquidphase is 0.25.

After polymerizing for 3 hours, the temperature of the autoclave isbrought to 45° C. while degassing it to a pressure of 3 bars.

Approximately 0.03 bar of hydrogen is then introduced and the pressureis adjusted, by means of propylene, to 3.1 bars and then, by addition ofethylene, to 4.6 bars.

The polymer (b) is obtained by polymerizing under these conditions for 1hour and by keeping the composition of the gaseous phase constant.

The molar fraction of ethylene in the liquid phase is 0.028 and that ofpropylene is 0.253.

A block copolymer is thus obtained, with a productivity prod of 3653,which exhibits the following properties:

Sol=3.2

AD=500

MFI=5.4

Ethylene content in the final block copolymer=9% by weight.

Examples 2 to 4

These examples illustrate the production of block copolymers accordingto the invention in which the polymer (a) is a homopolymer of propyleneand in which the polymer (b) is an ethylene-propylene copolymercontaining an α,ω-diene: 1,9-decadiene.

The catalytic solid used in carrying out these examples is that ofExample 1.

The block copolymer is obtained by repeating the procedure of Example Ibut by introducing the α,ω-diene after the degassing of the autoclave to3 bars for the preparation of the polymer (b).

The conditions for the production of these block copolymers as well astheir properties are reproduced in Table I.

                  TABLE I                                                         ______________________________________                                        Examples        2         3       4                                           ______________________________________                                        Preparation of the Polymer (b)                                                α,ω-Diene used (ml)                                                               5         10      50                                          Molar fraction of ethylene in                                                                 0.028     --      0.028                                       the liquid phase                                                              Molar fraction of propylene in                                                                0.253     --      0.253                                       the liquid phase                                                              Molar fraction of α,ω-diene in                                                    1.5 × 10.sup.3                                                                    --      0.015                                       the liquid phase                                                              Polymerization results                                                        prod            3653      3741    3787                                        Amount of polymer (b)                                                                         18        18      18                                          Amount of polymer (a)                                                                         82        82      82                                          Sol             1.7       1.4     1.2                                         AD              507       507     508                                         MFI             1         0.9     0.2                                         Ethylene content in the final                                                                 6         6       6                                           block copolymer (% by weight)                                                 ______________________________________                                    

Comparison of these results with those of Example 1 given by way ofreference enables the low level of soluble material observed when thepolymerization is carried out in the presence of α,ω-diene, as well asthe good morphology of the block copolymers obtained, to bedemonstrated.

Examination of the curves reproduced in the single figure clearly showsthat the block copolymers according to the present invention exhibit thephenomenon of stress hardening.

Example 5

Example 2 is repeated, except as regards the polymerization time for thestage for formation of the polymer (b) (1.5 hours) and as regards theamount of α,ω-diene used (20 ml).

The properties of the block copolymer obtained are:

prod=3833; Amount of polymer (a)=73; Amount of polymer (b)=27; Sol=2.2;AD=489; MFI=0.2; Ethylene content in the final block copolymer=12% byweight.

Example 6R

Example 5 is repeated, the introduction of the α,ω-diene being omitted.

The properties of the block copolymer obtained are:

prod=3833; Amount of polymer (a)=73; Amount of polymer (b)=27; Sol=4.0;AD=487; MFI=3.2; Ethylene content in the final block copolymer=12% byweight.

Reference Example 7R and Example According to the invention 8

A. Preparation of the Catalytic Solid

The catalytic solid is prepared as described in Example 1R, part A butthe final treatment with propylene being omitted.

B. Preparation of the Block Copolymers

Example 7R is carried out by repeating Part B of Example 1R. The blockcopolymer according to Example 8 is obtained by repeating Example 2. Theproperties of the block copolymers obtained are reproduced in Table IIbelow.

                  TABLE II                                                        ______________________________________                                        Examples           7R     8                                                   ______________________________________                                        prod               3339   3450                                                Amount of polymer (b)                                                                            18     18                                                  Amount of polymer (a)                                                                            82     82                                                  Sol                3.8    3                                                   AD                 486    488                                                 MFI                11.6   1.9                                                 Ethylene content in the                                                                          8      8                                                   final block copolymer                                                         Flex. Mod.         1350   1378                                                g                  680    675                                                 Izod               3.7    4.2                                                 Embrit. Temp.      -23    -33                                                 ______________________________________                                    

Comparison of these results enables the better impact strength/stiffnesscompromise of the block copolymers according to the invention to bedemonstrated.

What is claimed is:
 1. A propylene block copolymer, comprising:(a) 100parts by weight of a polymer (a) of propylene selected from homopolymersand copolymers of propylene not containing more than 60 by weight ofethylene and/or of an alpha-olefin having from 4 to 6 carbon atoms, and(b) from 1 to 100 parts by weight of a polymer (b) of ethylene selectedfrom copolymers of ethylene containing at least 30% and not more than90% by weight of propylene, the polymer (b) additionally containing fromapproximately 0.001 to approximately 20% by weight, with respect to thetotal weight of the block copolymer comprising polymer (A) of propyleneand polymer (B) of ethylene, of α,ω-diene-derived monomer units.
 2. Theblock copolymer according to claim 1, wherein the α,ω-diene containsfrom 6 to 30 carbon atoms.
 3. The block copolymer according to claim 2,wherein the α,ω-diene is selected from the croup consisting of1,6-heptadiene, 1-7-octadiene, 1,8-nonadiene, 1,9-decadiene,1,10-undecadiene, 1,11-dodecadiene, 1,12-tridecadiene and1,13-tetradecadiene.
 4. The block copolymer according to claim 3,wherein the α,ω-diene is 1,9-decadiene.
 5. The block copolymer accordingto claim 1, wherein the concentration of α,ω-diene-derived monomer unitsis from 0.02 to 10% by weight with respect to the total weight of theblock copolymer comprising polymer (A) of propylene and polymer (B) ofethylene.
 6. The block copolymer according to claim 1, comprising:100parts by weight of a homopolymer of propylene, and from 10 to 80 partsby weight of an ethylene copolymer containing from 40 to 60% by weightof propylene and in addition from approximately 0.02 to approximately 5%by weight with respect to polymer (b) of monomer units derived from anα,ω-diene.
 7. The block copolymer according to claim 1 wherein saidcopolymer exhibits stress hardening.
 8. The block copolymer according toclaim 1 exhibiting an MFI of less than 1 g/10 min.
 9. In a process forthe production of shaped articles by extrusion blow-moulding orinjection blow-moulding the improvement comprising so moulding a blockcopolymer according to claim
 1. 10. In process for the production ofshaped articles by thermoforming or coating articles, the improvementcomprising thermoforming or coating articles with a block copolymeraccording to claim
 1. 11. In a process for the formation of foams, theimprovement comprising forming a block copolymer according to claim 1.12. Block copolymer according to claim 1 exhibiting compatibilitybetween the polymers (a) and (b).
 13. A process for the production of ablock copolymer comprising at least two successive polymerization stagesin which a mixture of monomers is contacted with a catalytic system,under polymerizing conditions, comprising in a first stage, a mixture ofmonomer containing:from approximately 45 to 100% by weight of propyleneand which can in addition containup to approximately 5% by weight ofethylene and/or of an alpha-olefin having from 4 to 6 carbon atoms andup to approximately 50% by weight of α,ω-diene; and, in a second stage,a mixture of ethylene, of propylene and of α,ω-diene containing ethyleneand: up to approximately 90% by weight of propylene and up toapproximately 50% by weight of α,ω-diene, the minimum amount ofα,ω-diene being at least 0.005% by weight.
 14. The process according toclaim 13, applied to the production of a propylene block copolymercomprising:(a) 100 parts by weight of a polymer (a) of propyleneselected from homopolymers and copolymers of propylene not containingmore than 6% by weight of ethylene and/or of an alpha-olefin having from4 to 6 carbon atoms, and (b) from 1 to 100 parts by weight of a polymer(b) of ethylene selected from copolymers of ethylene containing at least30% and not more than 90% by weight of propylene, the polymer (b)additionally containing from approximately 0.001 to approximately 20% byweight, with respect to the total weight of the block copolymercomprising polymer (A) of propylene and polymer (B) of ethylene, ofα,ω-diene-derived monomer units.
 15. Process according to claim 13, inwhich the α,ω-diene is used only in the second stage.
 16. Processaccording to claim 13, in which the polymerization is carried out insuspension in an aliphatic hydrocarbon.
 17. The process according toclaim 16, in which the amounts of the monomers used are such that:in thefirst stage, the ratio of the molar fractions of ethylene and ofpropylene in the liquid phase is less than or equal to approximately0.015 and the ratio of the molar fractions of α,ω-diene and of propylenein the liquid phase is less than or equal to approximately 5 and in thesecond stage, the ratio of the molar fractions of ethylene and ofpropylene in the liquid phase is greater than or equal to approximately0.06 and less than or equal to approximately 0.14 and the ratio of themolar fractions of α,ω-diene and of propylene in the liquid phase isless than or equal to approximately
 5. 18. The process according toclaim 17, in which exclusively propylene is used in the first stage. 19.The process according to claim 13, in which the polymerization iscarried out by means of a catalytic system containing a complexed solidcomprising TiCl₃ and an activator chosen from organoaluminium compounds.20. The process according to claim 19, in which the complexed catalyticsolid comprising TiCl₃ has been subjected to a prepolymerizationtreatment so as to incorporate therein at least 50% by weight of polymerwith respect to the weight of TiCl₃.